广东揭汕潮地区城市群地震灾害及地震易损性分析

从历史最大地震烈度分布图分析,可知揭阳、汕头、潮州三市位于Ⅶ～Ⅷ度高地震烈度区。该城市群地震灾害有以下特点:市区发生破坏性地震的潜在危险性大;地震时市区地震烈度高,地震灾害大,损失严重。采用宏观经济易损性的地震损失分析方法,重演该区的历史破坏性地震。分析表明:抓好该区的防震减灾工作是保持社会和经济建设持续发展的一项重要工作。     

朝鲜2009年和2013年两次核爆的地震学特征对比研究

利用布设在长白山地区临时地震台站接收到的朝鲜核爆的波形资料,对2009年5月25日和2013年2月12日两次朝鲜核试验的地震学特征进行比较.震中距范围从145km到420km.采用P/S型谱比值方法识别朝鲜核爆,通过与2009年3月20日长春地震和2013年1月23日沈阳地震事件的比较,表明在频率大于3 Hz时P/S型谱比值能够有效识别发生在中朝边境地区的地下核试验.选定参考台站,利用区域震相Pg波的振幅谱比值计算朝鲜核爆至各台站路径上的相对衰减.结合介质速度模型,在一定程度上反映了长白山地区衰减情况,为进一步研究长白山地区衰减层析成像提供初始模型.     

Glacier retreat and climatic variability in the eastern Terskey–Alatoo, inner Tien Shan between the middle of the 19th century and beginning of the 21st century

Changes in the extent of glaciers and rates of glacier termini retreat in the eastern Terskey–Alatoo Range, the Tien Shan Mountains, Central Asia have been evaluated using the remote sensing techniques. Changes in the extent of 335 glaciers between the end of the Little Ice Age (LIA; mid-19th century), 1990 and 2003 have been estimated through the delineation of glacier outlines and the LIA moraine positions on the Landsat TM and ASTER imagery for 1990 and 2003 respectively. By 2003, the glacier surface area had decreased by 19% of the LIA value, which constitutes a 76 km² reduction in glacier surface area. Mapping of 109 glaciers using the 1965 1:25,000 maps revealed that glacier surface area decreased by 12.6% of the 1965 value between 1965 and 2003. Detailed mapping of 10 glaciers using historical maps and aerial photographs from the 1943–1977 period, has enabled glacier extent variations over the 20th century to be identified with a higher temporal resolution. Glacial retreat was slow in the early 20th century but increased considerably between 1943 and 1956 and then again after 1977. The post-1990 period has been marked by the most rapid glacier retreat since the end of the LIA. The observed changes in the extent of glaciers are in line with the observed climatic warming. The regional weather stations have revealed a strong climatic warming during the ablation season since the 1950s at a rate of 0.02–0.03 °C a^− 1. At the higher elevations in the study area represented by the Tien Shan meteorological station, the summer warming was accompanied by negative anomalies in annual precipitation in the 1990s enhancing glacier retreat. However, trends in precipitation in the post-1997 period cannot be evaluated due to the change in observational practices at this station. Neither station in the study area exhibits significant long-term trends in precipitation.     

Optical dating of aeolian and fluvial sediments in north Tian Shan range,China: Luminescence characteristics and methodological aspects

Loess and fluvial sand are important materials for dating river terraces and alluvial fans. This study focuses on the methodological aspects of dating loess and fluvial deposits from the northern flank of the Tian Shan range, China, using sand-sized quartz and potassium (K) feldspar. Luminescence characteristics of quartz and K-feldspar were studied for searching suitable dating procedures. Our results indicate that 1) most quartz aliquots were contaminated by feldspar, and were dated using a post-infrared optically stimulated luminescence (post-IR OSL) procedure. A Fast ratio acceptance threshold of 15 can be applied to select these aliquots with post-IR OSL signals dominated by quartz OSL; 2) the multi-elevated-temperature post-IR IR stimulated luminescence (MET-pIRIR) procedures are applicable for K-feldspar. A test dose of ∼30% of the natural dose is appropriate for dating of older (>10 ka) samples. An Age (T, t) plateau test can be used to evaluate the dating results; 3) for the loess samples, both quartz and K-feldspar were well bleached and are suitable for dating. Dating using K-feldspar is preferred for its higher efficiency; 4) for the fluvial sand samples, only the quartz grains were fully bleached. Single-aliquot dating of quartz gives reliable ages.     

青藏高原东缘新生代早期古应力环境:来自四川盆地西南缘磁组构的记录

四川盆地西南缘紧邻龙门山褶皱冲断带(青藏高原东边界)南段.该地区的新生代早期红层沉积记录了青藏高原东缘的隆升历史及构造演变.本研究选取四川盆地西南缘芦山地区古新统—下渐新统名山组—芦山组地层剖面为研究对象,利用磁组构方法,结合前人对研究区古地磁及构造变形的研究,恢复了该地区新生代早期的古应力方向.本研究获取了548块样品的磁组构数据,这些磁组构的磁面理与层面平行,产状校正后磁线理呈NE-SW方向(39°/219°),K₃主轴方向相对集中(为120.9°±1.3°),为弱应变背景下平行层缩短之前初始变形磁组构类型,主要形成于地层成岩阶段,未受到后期褶皱等构造变形的强烈改造.本研究认为芦山剖面磁组构结果记录了研究区新生代早期的构造变形信息:新生代早期龙门山褶皱冲断带南段及川西南盆地受NW-SE向的最大主应力控制.该地区新生代晚期及现今应力场与新生代早期一致,可能继承了新生代早期的应力体制,暗示龙门山作为青藏高原的东边界可能在新生代早期已经形成.     

新疆柴窝堡盆地南缘晚新生代陆源沉积物岩石磁学特征及其古环境意义

亚洲内陆晚新生代干旱化历史及其驱动机制是非常重要的科学问题。选择天山北麓柴窝堡盆地南缘乌鲁木齐河剖面为研究对象,基于磁性地层年代学研究建立的时间标尺,分析了该剖面碎屑沉积物岩石磁学特征及其控制因素,进一步探讨了柴窝堡盆地晚新生代古气候特征。磁性地层年代学研究约束乌鲁木齐河剖面底界年龄为~6.8 Ma,顶界年龄为~3.3 Ma。详细的岩石磁学测量及漫反射光谱分析结果表明,乌鲁木齐河剖面沉积物中磁性矿物主要包括磁铁矿、赤铁矿等,磁学参数χ_lf、χ_ARM、SIRM、S_-100mT、S_-300mT、 χ_ARM/SIRM等在~6.3 Ma、~5.2 Ma存在明显变化,揭示磁性矿物粒度、含量等存在相应变化,如在~6.3 Ma前后,磁性矿物颗粒逐渐变粗、含量降低;在~5.2 Ma前后,磁性矿物颗粒逐渐变细后趋于稳定、含量逐渐增多。基于稀土元素分析、沉积粒度与磁学参数相关性分析,认为沉积物源与沉积物粒度不是导致乌鲁木齐河剖面磁学性质变化的主要因素,自~6.8 Ma以来逐步干旱化的气候条件可能是导致该剖面磁学特征变化的重要原因。基于漫反射光谱分析得到的红度与亮度数据结果也揭示了同样的古气候特征。     

White mica trace element and boron isotope evidence for distinctive infiltration events during exhumation of deeply subducted continental crust

ABSTRACT

Previous study of subducted continental crust within the Luliang Shan terrane in Northwest China has documented metasomatic formation of thick, hydrated phengite + garnet-rich selvages at the interface between mafic eclogite blocks and quartzofeldspathic host gneiss. Whole rock concentrations of Cs and Ba within the selvage are enriched by two orders of magnitude relative to the eclogite blocks and host gneiss. We performed in situ ion microprobe analyses of Li, Be, B, Rb, Sr, Cs and Ba and δ¹¹B of phengite within the Luliang Shane terrane to better constrain the source(s) of the infiltrating fluid. The phengite within the selvage are enriched in Li, Cs and Ba and yield δ¹¹B values between ?30‰ and ?9‰, values that are lower than mantle values. High Ba/Rb, Cs/Rb coupled with low B/Be, B/Li and highly negative δ¹¹B values indicate that the high-pressure fluid that formed the selvage was derived from highly devolatilized rocks within the subduction channel. In contrast, muscovite, which crystallized in the adjacent host gneiss during a subsequent lower pressure phase of fluid infiltration at approximately 0.9 GPa depths, has much lower Li, Cs and Ba relative to the high-pressure phengite. These retrograde muscovite have very high concentrations of B (up to 5500 ppm) and Be (up to 50 ppm) and high (?2 to +8‰) δ¹¹B values that are consistent with crystallization from a fluid derived from shallower and less devolatilized regions of the subduction zone. Additional host gneiss samples, regionally distributed and kilometres away from the studied area lack the B-rich signature and indicate that the late stage fluids were likely localized to the region near the studied traverse.     

Multistage Enrichment of the Sawafuqi Uranium Deposit: New Insights into Sandstone-hosted Uranium Deposits in the Intramontane Basins of Tian Shan, China

Meso-Cenozoic intracontinental orogenic processes in the Tian Shan orogenic belt have significant effect on the sandstone-hosted uranium deposits in the intramontane basins and those adjacent to the orogen. The Sawafuqi uranium deposit, which is located in the South Tian Shan orogenic belt, is investigated to reveal the relationships between uranium mineralization and orogenies. Recent exploration results show that the Sawafuqi uranium deposit has tabular, stratiform, quasi-stratiform, and lens-like orebodies and various geological characteristics different from typical interlayer oxidation zone sandstone-hosted uranium deposits. Systematic studies of ore samples from the Sawafuqi uranium deposit using a variety of techniques, including thin section observation, α-track radiograph, electron microprobe and scanning electron microscope, suggest that uranium mineralization is closely related to pyrite and organic matter. Mineralization-related alterations in the host rocks are mainly silicification and argillation including kaolinite, illite(and illite-smectite mixed layer) and chlorite. Tree stages of mineralization were identified in the Sawafuqi uranium deposit:(i) uranium-bearing detritus and synsedimentary initial pre-enrichment;(ii) interlayer oxidization zone uranium mineralization; and(iii) vein-type uranium mineralization. The synsedimentary uranium pre-enrichment represents an early uranium enrichment in the Sawafuqi uranium deposit, and interlayer oxidation zone uranium mineralization formed the main orebodies, which are superimposed by the vein-type uranium mineralization. Combining the results of this study with previous studies on the Meso-Cenozoic orogenies of South Tian Shan, it is proposed that the synsedimentary uranium pre-enrichment of the Sawafuqi uranium deposit was caused by Triassic Tian Shan uplift, and the interlayer oxidation zone uranium mineralization occurred during the Eocence-Oligocene period, when tectonism was relatively quiet, whereas the vein-type uranium mineralization took place in relation to the strong orogeny of South Tian Shan since Miocene.     

大别山碧溪岭榴辉岩450 Ma年龄信息:石榴子石流体包裹体40Ar-39Ar定年初步结果

高压-超高压变质岩常含有过剩40Ar,排除过剩40Ar的干扰是获得可靠40Ar-39Ar年龄的关键.本文试图从流体包裹体40Ar-39Ar定年的角度,探讨榴辉岩40Ar-39Ar定年技术与过剩40Ar问题.采用真空击碎法提取流体包裹体,对碧溪岭浅色榴辉岩石榴子石进行40Ar-39Ar定年,获得了下降型年龄谱:最初9个阶段年龄谱总体上呈逐渐下降,表观年龄从2 226 Ma下降到753 Ma,这是次生包裹体(含过剩40Ar)与原生包裹体(不含过剩40Ar)混合的结果;第10阶段至第22阶段(末阶段),年龄谱呈平缓波动,表观年龄变化小,对应坪年龄为(449±18)Ma(2σ,39Ar占59.5%),这是微小的原生流体包裹体的贡献,此13个数据点在36Ar/40Ar-39Ar/40Ar图上构成线性关系很好的反等时线,对应的等时线年龄(448±34)Ma代表了石榴子石的结晶年龄,40Ar/36Ar初始比值(292±5)表明原生包裹体不含过剩40Ar.     

天山及邻区Vening Meinesz均衡重力异常特征及其动力学意义

本文基于Vening Meinesz区域均衡模型,通过试验不同参数计算Vening Meinesz均衡补偿深度,将其与CRUST1.0模型给出的莫霍面深度进行拟合,得到适应于天山及邻区的平均补偿深度、"地区性指标"以及区域补偿半径.结合地球重力场模型EIGEN-6C4与地形数据,利用球冠体积分方法进行地形效应、沉积层效应计算和均衡校正,得到了研究区的Vening Meinesz均衡重力异常.结果显示天山及邻区的均衡重力异常幅值在-110~120 mGal之间,表明了天山及周边盆地岩石圈所处于的均衡状态,同时揭示了研究区的壳幔密度分布特征.天山、塔里木盆地、准噶尔盆地等块体的地壳垂向形变可能部分地由均衡调整引起,且均衡调整趋势与地面形变测量结果相契合.通过对均衡重力异常成因的解释,从地壳均衡角度分析了该地区复杂的构造背景及其新生代以来的演化历程.